Various intravital sugar chains play an important role in a mechanism for sustaining activities and lives of living organisms. In order to specifically clarify the functions of such sugar chains, it is necessary to analyze the functions of the sugar chains based on a conjugate structure thereof. Functional analysis of the sugar chains is carried out by the following technique. The structure of a sugar chain is reproduced part by part by using oligosaccharide whose structure is elucidated, so as to clarify the relation between the structure of a whole sugar chain and its functions.
As the technique of the functional analysis of sugar chains, the surface plasmon resonance (hereinafter referenced to as SPR) method is known, for example. That is, the ligand conjugate containing the oligosaccharide which imitates a part of sugar chain is immobilized on the sensor chip surface. By using the sensor chip having oligosaccharide immobilized thereon, a substance, such as protein, which specifically interacts with an oligosaccharide are identified. This makes it possible to properly evaluate a biological activity based on the structure of the oligosaccharide.
Meanwhile, a single oligosaccharic molecule is not active enough. Therefore, it is necessary to implement a large number of molecules of oligosaccharide onto the sensor chip when evaluating a biological activity of an oligosaccharide. In other words, the use of a large number of molecules of oligosaccharide for analysis of interaction with a protein allows for evaluation of biological activity of oligosaccharide.
In view of this, the inventor of the present invention and the others have so far found a linker compound including molecules having therein (i) moiety capable of being immobilizable onto the surface of the sensor chip and (ii) moiety capable of taking in one or two units of oligosaccharide. Also, the inventor of the present invention and the other have so far found a ligand conjugate which includes the linker compound having one or two units of sugar chains of oligosaccharide introduced thereinto. Then, the inventor of the present invention and the others found that the use of such a ligand conjugate makes it possible to introduce a large number of molecules of oligosaccharide onto the sensor chip (for example, see Patent literature 1, Non-patent literature 1).
[Patent Literature 1]
Japanese Unexamined Patent Publication No. 836969/2003 (Tokukai 2003-836969; published on Mar. 19, 2003)
[Non-Patent Literature 1]
Tentative Lecture Proceedings II in the 79th Spring Meeting, Chemical Society of Japan, Mar. 15, 2001, p. 1042
However, the ligand conjugates described in the literatures are such that sugar (oligosaccharides) introducible to the ligand conjugates are limited to sulfated sugar synthesized by the inventor of the present invention and the others. The literatures does not describe whether or not commercially-available oligosaccharides having a reducing end, such as maltose, lactose, and the like, can be introduced into the ligand conjugate to form a sensor therewith. Moreover, it has been proposed to carry out the SPR measurement and then protein identification with the same sensor chip having the ligand conjugate described in the literatures immobilized thereon, in order to identify a protein bonded with the sugar chain on the chip. However, no technique that can give satisfactory data has not been established.
The present invention is accomplished in view of the aforementioned problems, and has an object to provide a novel ligand conjugate in which a commercially-available sugar having a reducing end is introduced, and a ligand carrier which can be used for protein identification.